(a) Technical Field of Invention
This invention relates to a polymeric film and, in particular, to a linear polyester film exhibiting improved flex-crack resistance.
(b) Background of the Art
Oriented films of linear polyesters, such as polyethylene terephthalate, are of utility in a wide range of applications including magnetic recording media--such as tapes and discs, as supporting substrates for light-sensitive emulsions, pressure-sensitive adhesives and metallic layers, as decorative drapes and electrical insulants, and particularly as packaging films.
In certain circumstances, in which an oriented polyester film is subjected to repeated flexing, the film structure may crack or develop pin holes which detract from the moisture and gas barrier characteristics of the film and may eventually lead to total failure of the film. It has therefore been proposed in U.S. Pat. No. 3,579,609 to improve the flex resistance of a biaxially oriented polyethylene terephthalate film by incorporating therein a minor amount of a solid, fusible heat-stable additive polymer comprising a polymer of a lower alpha mono-olefin such as ethylene, propylene, butylene and 4-methyl pentene, or an ethylene-vinylacetate copolymer, or polytetramethylene oxide.
We have now devised a polyester film exhibiting improved flex-crack resistance.